Induction heating



United States Patent 3,236,993 INDUCTION HEATING David Griiliths Jones,Cheltenham, England, assignor to Delapena & Son Limited, Cheltenham,England Filed May 6, 1963, Ser. No. 278,808

Claims priority, application Great Britain, May 5, 1962,

Claims. (Cl. 219-10.59)

This invention relates to induction heating and in particular to methodsof and apparatus for induction heating gears and other elements having atoothed or serrated periphery. The invention can be applied to heatingeither an external or internal periphery, and is of especiallyadvantageous application to the case hardening of gear teeth and thesplines of splined elements.

At present there are two general methods in use to produce a hardenedsurface of gear teeth employing induction heating. In the older of thesemethods the gear is encircled by a single or multi-turn helicalinductor, and when the surfaces reach the required temperature the gearis quenched in water or other suitable medium. This does not result intrue case hardening, as the teeth tend to be hardened throughout and dueto the mass effect the roots of the teeth are not sufficiently hot whenthe teeth themselves reach hardening temperature; as a result the rootsare not effectively hardened. There is also the so-called striationeffect which results in alternating relatively hot and cool bands roundthe gear, with consequent variations in the case hardness and depth. Theother method produces a hot line in a single tooth space, this linebeing scanned along the length of the gear and the scanning repeated foreach tooth space. This method produces a much more even case but formass production purposes has the disadvantage of being relatively slow,a disadvantage which it is the `object of the invention to materiallyreduce.

According to the invention an inductor for induction heating a toothedor serrated surface of an element, comprises a single turn currentcarrying loop generally profiled to suit the surface and havingprojections which project into the spaces between the teeth orserrations when the element and the inductor are coaxially arranged,each projection being associated with a U-shaped magnetic core whichstraddles the inductor loop with the free ends of the limbs of each coreextending in the same direction as the respective projection.

Preferably the cores are of laminated form to withstand thermal shockwhich can be great when rapid rates of heating are used. However, dustcomposition cores may be used, or they may be moulded from ferritematerial.

The laminations preferably lie in planes perpendicular to the adjacentpart of the current carrying loop.

According to a preferred feature of the invention the magnetic cores arehoused in slots formed in the surface of the current carrying loop.

Preferably the free ends of the limbs of each core extend somewhatbeyond the edge of the corresponding projection on the current carryingloop.

In use the inductor of the invention produces current loops in thespaces between the teeth or serrations and also a circulating currentwhich is induced round the complete periphery of the element. The effectof the circulating current may be reduced to a relatively low value bycutting away the inductor between the projections thereof, for exampleby machining slots in the inductor. The effect of these slots is toincrease the effective diameter of the inductor current path, leavingthe cores acting as fiux intensifiers in said spaces. The slots arepreferably filled with a ferro-magnetic material, for example ironlaminae. The axial Width of the inductor 3,236,993 Patented Feb. 22,1966 ice and the width of the cores are suitably designed to produceoverlapping circulating current paths at the roots 0f the teeth orserrations, such overlapping producing an additional heating effectwhere it is most needed.

According to another aspect of the invention a method of inductionheating an element with a toothed or serrated periphery comprises thesteps of arranging the element and a single turn annular inductor inaxial alignment, the inductor having spaced projections each associatedwith a U-shaped core which straddles the inductor with the ends of thecore limbs and the projections aligned with the spaces between the teethor serrations, energising the inductor to induce heating current loopsin the peripheral surface of the element in said spaces, and causingrelative traversing movement of the inductor and the element along thelength of the latter.

By the method of the invention heating current loops are produced ineach of said spaces, and when the inductor has completely traversed theelement the flanks of all the teeth or serrations are effectivelyheated. Preferably overlapping current loops are produced in each space,the overlapping of the loops producing an increased heating effect atthe roots of the teeth or serrations, thus compensating for the masseffect in those positions.

The invention may be performed in various ways and two specificembodiments will now be described -by way of example with reference t0the accompanying drawings, in which:

FIGURE l is a perspective view partly broken away showing part of aninductor according to the invention in position surrounding a gear to beheat treated,

FIGURE 2 is a plan view of the inductor of FIG- URE 1,

FIGURE 3 is a cross-sectional View on the line III-III in FIGURE 2,

FIGURE 4 is an enlarged fragmentary plan view showing the arrangement ofthe laminated cores on the current carrying loop, and

FIGURE 5 is a perspective view corresponding to FIG- URE l showing amodified form of the invention.

In these examples the inductors are designed for use in case hardeningan external toothed gear wheel. As seen in FIGURES l and 2 the inductorcomprises a single turn current-carrying loop in the form of a copperring 10 machined with an internal profile generally inverse to the gearprofile so providing projections which extend into the toothed spacesand lie closely -adjacent the tooth flanks of the gear when the gear andthe inductor are coaxially located.

The copper ring 10 is formed with radial slots on both annular faces andan axial slot on its external cylindrical surface, in the region of eachprojection. At each projection a U-shaped laminated ferro-magnetic coreis pressed into position in the slots, the core being so dimensionedthat the external surfaces of the laminations 11 are flush with theradial and external faces of the copper ring, as seen in FIGURE l. Thefree ends 12 of the limbs `of these laminations extend somewhat Ibeyondthe tips of the projections on the inductor loop (13 in FIGURE 3). Thespace between the projecting ends of the limbs may be filled with a heatresistant insulating material 14. It will be noted that the laminatedcores are supported over most of their length by the projections on thecopper ring and these projections also tend to weaken the magnetic fluxaround the inductor between ythe laminated cores and to intensify thefield between the tips of the limbs of the cores. This increases theheating effect at the roots of the teeth yon the gear wheel.

Between each of the projections the copper ring is slotted or cut backon its internal surface as shown at 15 and each slot so formed is filledwith a ferro-magnetic material, preferably iron laminations 16. Thisarrangement further reduces the magnetic flux adjacent the tips of theteeth on the gear wheel by providing a magnetic bypass around 4thecurrent-carrying loop.

The current-carrying loop may be provided with an internal cooling waterchannel 17 which is conveniently formed by machining an external groovein the loop and brazing a band of copper 18 around t-he externalsurface, before the laminated cores are applied.

The copper ring is radially split midway between two of the projectionsas shown in FIGURE 2 and provi-ded with terminal members 19, 20 by whichthe high frequency electric -current is applied. These terminals arealso formed with passages Z1, 22 by which cooling water is circulatedthrough the channel 17.

In the modification illustrated in FIGURE the current-carrying loop 23is formed with projections to lie between the teeth of the gear wheel,as in the previous example, but the laminated cores 24 are not housed inslots in the loop but are fitted over its external surface. Thisconstruction is suitable for specific applica-tions.

In some applications it is also desirable to provide a supply ofquenching `water and this -can readily be delivered by providingapertures communicating with the cooling water passage 17.

I claim:

1. An inductor -for induction heating a toothed or serrated surface ofan element, comprising a single turn current-carrying loop providing acontinuous conductive path with a gap between its ends, said inductorbeing generally profiled to suit the surface and having projectionswhich project into the spaces between the tee-th or serrations when theelement and the inductor are coaxially arranged, said projectionsextending radially outwardly a distance greater than the gaps betweensaid projections, and a plurality of U-shaped magnetic coresindividually :associated with said projections, each magnetic corestraddling the inductor loop with the free ends of the limbs of eachcore extending in the same direction as the respective projection andthe other ends of the limbs extendmg radially outwardly a distancegreater than the gaps between said projections.

2. An inductor as claimed in claim 1, in which the magnetic cores arelaminated.

3. An inductor as claimed in claim 2, in which the laminations lie inplanes perpendicular to the adjacent part of the current carrying loop.

4t. An inductor as claimed in claim 1, in which the free ends of thelimbs of each core extend :somewhat beyond the edge of the correspondingprojection on the current-carrying loop.

5. An inductor as claimed in claim 1, in which the axial dimensions ofthe inductor loop and the axial spacing lbetween the limbs of each core[are appreciably smaller than the axial dimensions of the element to beheated so that overlapping circulating current paths are induced in thesurface of the element.

6. An inductor for induction heating the peripheral surface of a toothedarticle such as a gear wheel, comprising a single turn conductor loopproviding a continuous conductive path with a gap between its ends,lsaid inductor being profiled to suit the surface and coaxially surroundthe latter, said conductor loop having spaced projections which projectinto the spaces between the teeth on said surface and radial surfaceslots aligned with said projections, said projections extending radiallyoutwardly a distance greater t-han the gaps between said projections,and a plurality of U-shaped magnetic cores engaging said slots andstraddling the conductor loop with the free ends of the limbs of eachcore extending in the same direction ts the respective projection andslightly d beyond the edge thereof and the other ends of the limbsextending radially outwardly a distance greater than the gaps betweensaid projections.

7. An inductor for induction heating a toothed or serrated surface of anelement, comprising a single turn current-carrying loop providing acontinuous conductive path with a gap between its ends, said inductorbeing generally proled to suit the surface and having projections whichproject into the spaces between the teeth or serrations when the elementand the inductor are coaxially arranged, said projections extendingradially outwardly a distance greater than the gaps between saidprojections, the loop being cut away between the projections so as toreduce the heating effect at the tip of eac-h tooth on the element and aplurality of U-shaped magnetic cores individually associated with saidprojections, each magnetic core straddling the inductor loop with thefreer ends of the limbs of the core extending in the same direction asthe `respective projection and the other ends of the limbs extendingradially outwardly a distance greater than the gaps between saidprojections.

8. An inductor for induction heating a toothed or serrated surface of anelement, comprising -a single turn current-carrying loop generallyprofiled to suit the surface and having projections which project intothe spaces between the teeth or serrations when the element and theinductor are coaxially arranged, the loop being formed with slotsbetween the projections so as to reduce the -heating effect at the tipof each toot-h on the element, a tilling of ferro-magnetic material ineach such slot, land a plurality of U-shaped magnetic cores individuallyassociated with said projections, each magnetic core straddling theinductor loop with the free ends of the limbs of the core extending inthe same direction vas the respective projection.

9. An inductor according to claim 8, wherein each filling offerro-magnetic material is in the form of iron laminations.

10. An inductor for induction heating a toothed peripheral surface of anelement such as a gear wheel comprising a single turn current-carryingloop providing a continuous c-onductive path with a gap between itsends, said inductor being generally profiled to suit and coaxiallysurround the :surface and having projections whichl project into thespaces between the Iteeth or serrations when the element and theinductor are coaxially arranged, said projections extending radiallyoutwardly a distance greater than the gaps between said projections, anda plurality of U-shaped laminated magnetic cores individually associatedwith said projections, each magnetic core being disposed radially of andstraddling the inductor loop with the free ends lof the limbs of eachcore extending in the same direction as the respective projections andthe other ends of the limbs extending radially outwardly a distancegreater than the gaps 'between said projections.

References Cited by the Examiner UNITED STATES PATENTS 2,761,048 8/1956Tudbury 219-10.43 2,857,154 10/1958 Jones 219-1059 3,121,780 2/1964Mucha et al. 12.19-10.79

FOREIGN PATENTS 892,353 8/1953 Germany.

904,804 1/ 1954 Germany.

576,791 4/ 1946 Great Britain.

775,463 5/1957 Great Britain.

RICHARD M. WOOD, Primary Examiner, L. H. BENDER, Assistant Examiner.,

1. AN INDUCTOR FOR INDUCTION HEATING A TOOTHED OR SERRATED SURFACE OF ANELEMENT, COMPRISING A SINGLE TURN CURRENT-CARRYING LOOP PROVIDING ACONTINUOUS CONDUCTIVE PATH WITH A GAP BETWEEN ITS ENDS, SAID INDUCTORBEING GENERALLY PROFILED TO SUIT THE SURFACE AND HAVING PROJECTIONSWHICH PROJECT INTO THE SPACES BETWEEN THE TEETH OR SERRATIONS WHEN THEELEMENT AND THE INDUCTOR ARE COAXIALLY ARRANGED, SAID PROJECTIONSEXTENDING RADIALLY OUTWARDLY A DISTANCE GREATER THAN THE GAPS BETWEENSAID PROJECTIONS, AND A PLURALITY OF U-SHAPED MAGNETIC CORESINDIVIDUALLY ASSOCIATED WITH SAID PROJECTIONS, EACH MAGNETIC CORESTANDING THE INDUCTOR LOOP WITH THE FREE ENDS OF THE LIMBS OF EACH COREEXTENDING IN THE SAME DIRECTION AS THE RESPECTIVE PROJECTION AND THEOTHER ENDS OF THE LIMBS EXTENDING RADIALLY OUTWARDLY A DISTANCE GREATERTHAN THE GAPS BETWEEN SAID PROJECTIONS.